Some information for those skeptics
I know of many people who are skeptical about this idea, but I'm proof that they are thinking too much.
This is with use of a home theater reciever in a car, obviously getting the signal from the computer, and then sending out sound to the speakers.
First things first, get an ohmeter and check the impedance of your speakers, most home theater amps are 4ohm front min and 6ohm for the rest. Unless you get a really high quality amp, one of which I havent come by.
Why put a home theater amp in your car?
Well for one, if you are using a computer, get a sound card or something with a optical output. And make sure your amp can take the input. That way you get a pure lossless sound. What makes optical better than regular rca or even digital coax line is that it doesnt need X for voltage, optical is just the signal, no need to "amplify" it in any way. (On car HU [head unit] you have a preout usually right? Well they range anywhere from typically 2.5V to 4.4V. The higher the voltage the crisper the quality. Optical uses the highest quality at all times)
Secondly its cheap. Think about it, you can power 7 speakers in your car and a subwoofer(this one needs its own power) off of a $400, even $150 if you arent looking for high quality or 7.1.
And most importantly because you can. Thats what the whole "putting stuff into your car that shouldnt be in there" scene. Why stop at a computer? If you are running an inverter, more power to you, just make sure its capable of the max wattage on the amp + your computer (if its run on the inverter) and your set.
Now about the skeptical part, obviously car audio equipment is built a little differently than home audio stuff to make it more durable in the weather. But really, what can you change to make things more durable? Going from extremely cold to normal operating temp all the time isnt good for anything really, things will break down down the road and its something you have to deal with. But just make sure you get yourself a decent quality amp, around the 300-500 range with the functionality that you need (X channel stereo for playing 2 channel music through all your speakers, and dts decoding and what not incase you throw in a dvd)
So the main issue is that home audio components arent meant to go through the cold. Its been -40C in saskatoon a couple days now and it fires up perfect. (I have problems with hard drive freezing when its this cold, but that totally unrelated) if you go into my car after it sat overnight in the cold, and turn on my amp and play the radio (because its right there as soon as you turn on the amp) it plays, and it plays with perfect quality, no slowdowns, cutouts or anything. And it runs all the time. Gets the optical signal from my platinum bay and it sounds incredible (when its not on the radio)
An amp is an amp, it doesnt matter who makes it, or if its meant for home use or car, all it does is amplify a signal. So why spend 1000+ for an optical input 4.1 channel car audio amp, when you can get more for less?
I used lightning audio 12awg wiring from the amp to my 4 speakers and a thick rca cable for the sub preout (which is 4V by the way, better than my 2.5V on my JVC mp3 deck) and it sounds awesome.
Using this home theater amp still on my stock "premium" speakers was a HUGE increase in quality, no distortion, and with a home theater amp you can customize almost everything from speaker distance (delays) to individual gains on each speaker.
Just so you know, dont be afraid to use a HT reciever in your car. I've been running a Yamaha RX-v450 for over a month through brutal weather and I havent had a single problem whatsoever with it. It may not be enough time to tell if something will go, but I am extremely happy with it